Visual feedback and age affect upper limb reaching accuracy and kinematics in immersive virtual reality among healthy adults.

This cross-sectional study aimed to evaluate the effect of visual feedback, age and movement repetition on the upper limb (UL) accuracy and kinematics during a reaching task in immersive virtual reality (VR). Fifty-one healthy participants were asked to perform 25 trials of a reaching task in immersive VR with and without visual feedback of their hand. They were instructed to place, as accurately and as fast as possible, a controller held in their non-dominant hand in the centre of a virtual red cube of 3 cm side length. For each trial, the end-point error (distance between the tip of the controller and the centre of the cube), a coefficient of linearity (CL), the movement time (MT), and the spectral arc length of the velocity signal (SPARC), which is a movement smoothness index, were calculated. Multivariate analyses of variance were conducted to assess the influence of visual feedback, age and trial repetition on the average end-point error, SPARC, CL and MT, and their time course throughout the 25 trials. Providing visual feedback of the hand reduced average end-point error ( P  < 0.001) and MT ( P  = 0.044), improved SPARC ( P  < 0.001) but did not affect CL ( P  = 0.07). Younger participants obtained a lower mean end-point error ( P  = 0.037), a higher SPARC ( P  = 0.021) and CL ( P  = 0.013). MT was not affected by age ( P  = 0.671). Trial repetition increased SPARC ( P  < 0.001) and CL ( P  < 0.001), and reduced MT ( P  = 0.001) but did not affect end-point error ( P  = 0.608). In conclusion, the results of this study demonstrated that providing visual feedback of the hand and being younger improves UL accuracy and movement smoothness in immersive VR. UL kinematics but not accuracy can be improved with more trial repetitions. These findings could guide the future development of protocols in clinical rehabilitation and research.

Is cognition considered in post-stroke upper limb robot-assisted therapy trials? A brief systematic review.

The aim of this systematic review was, first, to determine whether or not individuals with cognitive deficits after stroke were enrolled in trials that investigated upper limb robot-assisted therapy effectiveness, and, second, whether these trials measured cognitive outcomes. We retrieved 6 relevant systematic reviews covering, altogether, 66 articles and 2214 participants. Among these 66 clinical trials, only 10 (15%) enrolled stroke participants with impaired cognition, whereas 50 (76%) excluded those with impaired cognition. The remaining six trials (9%) were classified as unclear as they either excluded individuals unable to understand simple instructions or did not specify if those with cognitive disorders were included. Furthermore, only 5 trials (8%) used cognitive measures as outcomes. This review highlights a lack of consideration for individuals with cognitive impairments in upper limb robotic trials after stroke. However, cognition is important for complex motor relearning processes and should not be ignored.

Effect of upper limb botulinum toxin injections on impairment, activity, participation, and quality of life among stroke patients.

BACKGROUND AND PURPOSE: The purpose of this study was to study the effect of Botulinum toxin type A (BoNT-A) injections in spastic upper limb muscles on impairment, activity, participation and quality of life in chronic stroke patients. METHODS: BoNT-A (Dysport) was injected into several upper limb spastic muscles in a group of 20 patients. Neurological impairment (muscle tone and strength, dexterity, SIAS), activity (ABILHAND), participation (SATIS-Stroke), and quality of life (SF36) were assessed before and 2 months after the injections. RESULTS: BoNT-A injections improved muscle tone, but had no impact on dexterity, manual ability, social participation, and quality of life. CONCLUSIONS: In this study, BoNT-A injections in spastic upper limbs significantly reduced neurological impairments, but had no functional impact.

Reproducibility of the ABILOCO questionnaire and comparison between self-reported and observed locomotion ability in adult patients with stroke.

OBJECTIVES: To test the reproducibility of the ABILOCO questionnaire. To validate the patient self-reporting method and the third-party assessment of the stroke patients' locomotion ability by a treating physical therapist. DESIGN: Prospective study. SETTING: University hospital. PARTICIPANTS: Adult stroke patients (N=28; 59+/-13y). The time since stroke ranged from 3 to 253 weeks. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: The ABILOCO questionnaire. RESULTS: The results of patient self-assessment and the results of the third-party assessments by the physiotherapists at a 2-week interval were highly correlated (intraclass correlation coefficient [ICC]=.77 and ICC=.89, respectively). The results of the patient self-assessment and the third-party assessment by the physical therapist were both well correlated to assessment by an independent medical examiner who observed the patient during the 13 ABILOCO activities (ICC=.69 and ICC=.87, respectively). CONCLUSIONS: The use of ABILOCO as a self-reporting questionnaire is a valid and reproducible method for assessing locomotion ability in patients with stroke in daily clinical practice and research.

Evaluation of manual ability in stroke patients in Benin: cultural adaptation and Rasch validation of the ABILHAND-Stroke questionnaire.

BACKGROUND: ABILHAND is a self-reported questionnaire assessing manual ability. It was validated and calibrated using the Rasch analysis for European stroke patients. After a stroke, performing upper limb activities of daily living is influenced by personal and environmental contextual factors. It is thus important to conduct a contextual validation to use this questionnaire outside of Europe. AIM: The aim of this study was to perform a cross cultural validation of the ABILHAND-Stroke questionnaire for post-stroke patients living in Benin, a West-African country. DESIGN: Observational cross-sectional study. SETTING: Outpatient rehabilitation centres. POPULATION: 223 Beninese chronic stroke patients. METHODS: The experimental questionnaire was made of 59 items evaluating manual activities. Patients had to estimate their difficulty of performing each activity according to four response categories: impossible, very difficult, difficult and easy. For construct validity analysis, patients were also evaluated with other assessment tools: Box and Block Test, the motor subscale of the Functional Independence Measure, the Stroke Impairment Assessment Set, and ACTIVLIM-Stroke. Data were analysed with the Rasch partial credit model. RESULTS: The response categories very difficult and difficult were merged and the number of response categories was reduced from 4 to 3 (impossible, difficult and easy). The Rasch analyses selected 16 bimanual activities that fit the Rasch model (chi square=42.35; P=0.10). The item location ranged from -1.10 to 2.24 logits. The standard error ranged from 0.15 to 0.22 logits. There is no differential item functioning between subgroups (age, sex, dexterity, affected side, time since stroke). The person separation index is 0.82. The questionnaire can measure 3 levels of manual ability, similarly to the occidental version. CONCLUSIONS: The ABILHAND-stroke is a Rasch validated, unidimensional and invariant questionnaire to assess manual ability among Beninese patients. The ordinal score can be transformed into linear score using a conversion table. CLINICAL REHABILITATION IMPACT: This assessment tool is clinically relevant in Benin, a developing country, since it requires no specific equipment or training. It should promote and standardize assessments for stroke patients in clinical practice and research in this African country.

Effect of simultaneous botulinum toxin injections into several muscles on impairment, activity, participation, and quality of life among stroke patients presenting with a stiff knee gait.

BACKGROUND AND PURPOSE: Walking is an essential activity for daily life and social participation, and it is frequently limited after stroke. A lack of knee flexion during the swing phase (stiff knee) is one of the impairments that restrict walking ability among patients with hemiparetic spasticity. Our purpose was to study the effect of Botulinum toxin type A (BoNT A) injections in several spastic muscles on the impairment, activity, participation, and quality of life of patients with chronic stroke presenting with a stiff knee gait. METHODS: Twenty chronic hemiparetic poststroke patients with stiff knee gait and ability to walk on a treadmill were recruited. BoNT A was injected into several spastic muscles: the rectus femoris (200 U), semitendinosus (100 U) and triceps surae (200 U). Patients' neurological impairments (Ashworth scale, Duncan-Ely test, Stroke Impairment Assessment Set, and instrumented gait analysis), activity (ABILOCO and 10-m walking test), and participation (SATISPART-Stroke and 36-item Short-Form Health Survey) were assessed before and 2 months after the injection. RESULTS: BoNT A injection reduced the impairments. It improved Stroke Impairment Assessment Set (56.5 [48-63] to 56.5 [52.5 to 63]; P<0.001), reduced rectus femoris muscle tone (2 [1 to 2.5] to 0 [0 to 1]; P<0.001), and reduced semitendinosus muscle tone (1 [1 to 1.5] to 1 [0 to 1]; P<0.001). Gait analysis demonstrated increased knee flexion during the swing phase (22+/-19 degrees to 27+/-16 degrees ; P=0.03), decreased external mechanical work (0.66+/-0.38 to 0.59+/-0.25 J kg(-1) m(-1); P=0.04), and demonstrated a lower energy cost (5.8+/-1.9 to 4.9+/-1.9 J kg(-1) m(-1); P=0.03). The patients' locomotion ability was improved (2.2+/-1.9 to 3.2+/-2.1 logits; P=0.03). The participation and quality of life remained unchanged. CONCLUSIONS: BoNT A injections in several muscles improved the stiff knee gait and the locomotion ability in adult stroke patients.

Effect of botulinum toxin injection in the rectus femoris on stiff-knee gait in people with stroke: a prospective observational study.

OBJECTIVE: To study the effect of botulinum toxin type A (BTX-A) injection in the rectus femoris on the decreased knee flexion during the swing phase of gait (stiff-knee gait) in people with stroke. DESIGN: Intervention study (before-after trial) with an observational design. SETTING: Outpatient rehabilitation clinic and gait laboratory. PARTICIPANTS: Nineteen chronic hemiparetic adults presenting with stiff-knee gait. INTERVENTION: Injection of 200 U of BTX-A (Botox) into the rectus femoris. MAIN OUTCOME MEASURES: Before and 2 months after BTX-A rectus femoris injection: Stroke Impairment Assessment Set (SIAS), Duncan-Ely test, and an instrumented gait analysis. RESULTS: Median SIAS score improved from 53 (range, 36-65) to 57 (range, 42-70) (signed-rank test, P=.005) and the Duncan-Ely score from 3 (range, 1-3) to 1 (range, 0-3) (P<.001). In gait analysis, mean (+/- standard deviation) maximum knee flexion improved from 26 degrees +/-13 degrees to 31 degrees +/-14 degrees during the swing phase (paired t test, P<.001), knee flexion speed at toe-off improved from 82 degrees +/-63 degrees to 112 degrees +/-75 degrees/s (P=.009), and knee negative joint power (eccentric muscular contraction) improved from -.27+/-.23 to -.37+/-.26 W/kg (P<.001). The 4 patients who almost did not flex the knee (<10 degrees) before the BTX-A rectus femoris injection did not improve after the injection. The other 14 patients who flexed the knee more than 10 degrees before the BTX-A rectus femoris injection decreased the walking energy cost from 5.4+/-1.6 to 4.6+/-1.3 J x kg(-1) x m(-1) (P=.006). CONCLUSIONS: BTX-A rectus femoris injection may be beneficial in patients with a stiff-knee gait after stroke, particularly in patients with some knee flexion (>10 degrees).

ABILOCO: a Rasch-built 13-item questionnaire to assess locomotion ability in stroke patients.

OBJECTIVE: To develop a questionnaire (ABILOCO), based on the Rasch measurement model, that can assess locomotion ability in adult stroke patients (International Classification of Functioning, Disability and Health activity domain). DESIGN: Prospective study and questionnaire development. SETTING: A faculty hospital. PARTICIPANTS: Adult stroke patients (N=100) (age, 64+/-15y). The time since stroke ranged from 1 to 260 weeks. INTERVENTION: A preliminary questionnaire included 43 items representing a large sample of locomotion activities. This questionnaire was tested on the 100 stroke patients, and their responses were analyzed using the Rasch model (RUMM 2020 software) to select items that had an ordered rating scale and fitted a unidimensional model. MAIN OUTCOME MEASURE: The ABILOCO questionnaire. RESULTS: The retained items resulted in a 13-item questionnaire, which includes a wide range of locomotion abilities well targeted to the sample population, leading to good reliability (R=.93). The item calibration was independent of age, sex, time since stroke, and affected side. The concurrent validity of ABILOCO was also investigated by comparing it with well-known, criterion standard scales (Functional Walking Category, Functional Ambulation Categories, item 12 of the FIM instrument evaluating walking ability) and the walking speed measured with the 10-meter walk test. CONCLUSIONS: The ABILOCO questionnaire presents good psychometric qualities to measure locomotion ability in adult stroke patients. Its range and measurement precision make it attractive for clinical use throughout the rehabilitation process and for clinical research.

Gastrointestinal risk assessment in patients requiring non-steroidal anti-inflammatory drugs for osteoarthritis: The GIRANO study.

OBJECTIVE: To evaluate gastrointestinal risk profiles in patients with osteoarthritis who are currently being treated, or who are candidates for treatment, with a non-steroidal anti-inflammatory drug. METHODS: Patients with osteoarthritis treated by primary care physicians or physical and rehabilitation medicine (PRM) specialists in Belgium and Luxembourg were scored for gastrointestinal risk profile, low, moderate or high, based on the presence of gastrointestinal risk factors. These included advanced age, gastrointestinal history, comorbidities, medication use, smoking, and alcohol consumption. Use of gastro-protective agents (proton pump inhibitors) was also assessed. RESULTS: A total of 190 primary care physicians and PRM specialists provided data on 885 patients. A large majority of patients were rated high-risk gastrointestinal (77.8%), with fewer moderate (19.4%) or low (2.8%) risk. The proportion of high-risk patients treated by PRM specialists was significantly lower than that treated by primary care physicians (64.7% vs 79.9%; p < 0.0001). Only 37.0% of high-risk patients received proton pump inhibitors co-prescription with a non-steroidal anti-inflammatory drug. CONCLUSION: A high prevalence of elevated gastrointestinal risk was found in this survey of patients with osteoarthritis who were current or candidate users of non-steroidal anti-inflammatory drugs. This appears to be insufficiently recognized, as preventative gastro-protective co-treatment was infrequently prescribed. Careful assessment of gastrointestinal risk factors should be made before prescribing non-steroidal anti-inflammatory drugs, with treatment tailored to the patient's gastrointestinal risk profile.

Age Effects on Upper Limb Kinematics Assessed by the REAplan Robot in Healthy Subjects Aged 3 to 93 Years.

Kinematics is recommended for the quantitative assessment of upper limb movements. The aims of this study were to determine the age effects on upper limb kinematics and establish normative values in healthy subjects. Three hundred and seventy healthy subjects, aged 3-93 years, participated in the study. They performed two unidirectional and two geometrical tasks ten consecutive times with the REAplan, a distal effector robotic device that allows upper limb displacements in the horizontal plane. Twenty-six kinematic indices were computed for the four tasks. For the four tasks, nineteen of the computed kinematic indices showed an age effect. Seventeen indices (the accuracy, speed and smoothness indices and the reproducibility of the accuracy, speed and smoothness) improved in young subjects aged 3-30 years, showed stabilization in adults aged 30-60 years and declined in elderly subjects aged 60-93 years. Additionally, for both geometrical tasks, the speed index exhibited a decrease throughout life. Finally, a principal component analysis provided the relations between the kinematic indices, tasks and subjects' age. This study is the first to assess age effects on upper limb kinematics and establish normative values in subjects aged 3-93 years.

Temporal organization of stride duration variability as a marker of gait instability in Parkinson's disease.

OBJECTIVE: Gait instability and fall risk are major concerns in Parkinson's disease. This study shows that the temporal organization of gait variability can represent a marker of gait instability that complements standard assessment of motor deficits in Parkinson's disease. METHODS: Temporal organization (long-range autocorrelation; LRA) of stride duration variability, collected from 20 persons with Parkinson's disease walking overground at a comfortable speed, was studied. The presence of LRA was based on the scaling properties of the series variability and the shape of the power spectral density. Simultaneously, measures of neurological impairment (MDS-UPDRS), balance (BESTest), and balance confidence (ABC-Scale) were collected. To precisely identify the relationship between LRA and functional measures, correlation coefficients were applied. RESULTS: Degradation of LRA was strongly correlated with other clinical scores, in such a way that the temporal organization of gait variability was more random for patients presenting with greater motor impairments. Importantly, these measures were relatively independent of age, and gait speed, thus they can be applied to a wide clinical population.  Conclusion: The findings of this study emphasize that temporal organization of gait variability is related to degree of functional impairment in Parkinson's disease. LRA may thus be regarded as an objective and quantitative measure of gait stability for both clinical practice and research.

Paradoxical effect of digital anaesthesia on force and corticospinal excitability.

The role played by sensory information in maintaining motor cortical representations is still incompletely understood. We investigated the effect of digital anaesthesia of the index finger and thumb on the amplitude of motor evoked potentials to transcranial magnetic stimulation (TMS) recorded from the first dorsal interosseus, F-wave response probability and maximal key pinch force. Whereas digital anaesthesia led to a 29% decrease in maximal force, both motor evoked potential amplitudes and F-wave probability remained unchanged. This dramatic decrease in maximal voluntary contraction following digital anaesthesia may result from a lack of proper sensory feedback during the task.

Effect of the rectus femoris motor branch block on post-stroke stiff-legged gait.

Six hemiparetic stroke patients presenting with a stiff-legged gait underwent a motor branch block of rectus femoris (RF). A gait analysis, including synchronous kinematic, dynamic, energetic recordings was performed before and after motor branch block of RF. The electrical activity of RF, Vastus Medialis, Vastus Lateralis, Vastus Intermedius was also recorded. Before nerve block, the sagittal kinematic data showed a decrease in both the mean maximum knee angular displacement during swing phase and the mean angular knee velocity at toe-off. In the sagittal kinetic data, the mean knee extension moment was increased. The mean mechanical work, internal and external work, was increased and the mean energy cost was also decreased. After the motor branch block of Rectus Femoris, the sagittal mean knee angular displacement and the mean internal work of the gait were significantly improved.

Feasibility of a self-rehabilitation program for the upper limb for stroke patients in Benin.

INTRODUCTION: Stroke is a major cause of disability and represents a very high cost in developing countries. Self-rehabilitation programs represent a new and original treatment for stroke patients, likely to reduce upper limb impairments and improve activity and participation. The goal of this study is to evaluate the feasibility of a self-rehabilitation protocol in Benin. METHODS: Twelve chronic stroke patients carried out the upper limb self-rehabilitation program (3 hours/day, 5 days/week for 2 weeks). The performance of these patients was evaluated before and after the self-rehabilitation program, by measuring the number of exercises that patients were able to achieve during a three-hour session, and by assessing their gross manual dexterity. RESULTS: Twelve patients were effectively able to complete the entire program. The number of unimanual exercises and self-mobilizations performed during a three-hour session as well as the score of the Box and Block test were improved by the self-rehabilitation program (P<0.05). DISCUSSION AND CONCLUSION: Self-rehabilitation programs are feasible and inexpensive as they do not involve a therapist. It is then a promising approach in stroke rehabilitation, particularly in developing countries, where rehabilitation costs are usually supported by patients.

Age Effects on Upper Limb Kinematics Assessed by the REAplan Robot in Healthy School-Aged Children.

The use of kinematics is recommended to quantitatively evaluate upper limb movements. The aims of this study were to determine the age effects on upper limb kinematics and establish norms in healthy children. Ninety-three healthy children, aged 3-12 years, participated in this study. Twenty-eight kinematic indices were computed from four tasks. Each task was performed with the REAplan, a distal effector robotic device that allows upper limb displacements in the horizontal plane. Twenty-four of the 28 indices showed an improvement during childhood. Indeed, older children showed better upper limb movements. This study was the first to use a robotic device to show the age effects on upper limb kinematics and establish norms in healthy children.

Box and block test in Beninese adults.

OBJECTIVE: To determine the Box and Block Test norm in a sub-Saharan population and to compare these data with published norms for North American adults. METHODS: A total of 692 healthy Beninese people, age range 20-85 years, were recruited. These subjects were asked to perform the Box and Block Test with both hands. RESULTS: Box and Block Test scores (mean and standard deviation (SD)) for women and men were, respectively, 81.3 (15.4) and 79 (16.6) for the dominant hand and 73.2 (13.7) and 72 (14.8) for the non-dominant hand. Mean Box and Block Test scores ranged from 89.1 (12.7) for people under the age of 25 years to 55.23 (10.5) for people over the age of 74 years. DISCUSSION: Manual dexterity was better for women than men, for dominant hand than non-dominant hand, and for younger subjects. In comparison with published results for US subjects, Beninese subjects had better dexterity below the age of 50 years in both sexes for the right hand and worse dexterity over 64 years of age in both sexes for the right hand. CONCLUSION: Developing and validating outcome scales in Africa will help to improve functional assessment of African populations in clinical practice and research.

Upper limb robot-assisted therapy in cerebral palsy: a single-blind randomized controlled trial.

BACKGROUND: Several pilot studies have evoked interest in robot-assisted therapy (RAT) in children with cerebral palsy (CP). OBJECTIVE: To assess the effectiveness of RAT in children with CP through a single-blind randomized controlled trial. PATIENTS AND METHODS: Sixteen children with CP were randomized into 2 groups. Eight children performed 5 conventional therapy sessions per week over 8 weeks (control group). Eight children completed 3 conventional therapy sessions and 2 robot-assisted sessions per week over 8 weeks (robotic group). For both groups, each therapy session lasted 45 minutes. Throughout each RAT session, the patient attempted to reach several targets consecutively with the REAPlan. The REAPlan is a distal effector robot that allows for displacements of the upper limb in the horizontal plane. A blinded assessment was performed before and after the intervention with respect to the International Classification of Functioning framework: body structure and function (upper limb kinematics, Box and Block test, Quality of Upper Extremity Skills Test, strength, and spasticity), activities (Abilhand-Kids, Pediatric Evaluation of Disability Inventory), and participation (Life Habits). RESULTS: During each RAT session, patients performed 744 movements on average with the REAPlan. Among the variables assessed, the smoothness of movement (P < .01) and manual dexterity assessed by the Box and Block test (P = .04) improved significantly more in the robotic group than in the control group. CONCLUSIONS: This single-blind randomized controlled trial provides the first evidence that RAT is effective in children with CP. Future studies should investigate the long-term effects of this therapy.

Variability of human gait: effect of backward walking and dual-tasking on the presence of long-range autocorrelations.

Information from the central and peripheral nervous systems is continuously integrated to produce a stable gait pattern. However, stride duration fluctuates in a complex manner in healthy subjects, exhibiting long-range autocorrelations that can span over hundreds of consecutive strides. The present study was conducted to explore the mechanisms controlling the long-term fluctuation dynamics of gait. In the first part of the study, stride duration variability was evaluated on a treadmill during forward (FW) and backward walking (BW). Despite the modification of the biomechanical constraints imposed on the locomotor system, the characteristics of the long-range autocorrelations remained unchanged in both modes of locomotion (FW: H = 0.79 ± 0.04 and α = 0.58 ± 0.13; BW: H = 0.79 ± 0.11 and α = 0.53 ± 0.25). In the second part of the study, stride duration variability was assessed while the subjects were performing a dual-task paradigm that combined gait and mental calculation. The long-term variability of stride duration was similar during usual walking (H = 0.80 ± 0.06 and α = 0.57 ± 0.13) and in dual-tasking (H = 0.77 ± 0.06 and α = 0.52 ± 0.16), whereas walking altered the performance of the cognitive task. Hence, the biomechanical and cognitive interferences imposed in the present study were not sufficient to induce a modification of the long-range autocorrelations highlighted in walking variability. These observations underline the robustness of the long-range autocorrelations.

Using the robotic device REAplan as a valid, reliable, and sensitive tool to quantify upper limb impairments in stroke patients.

OBJECTIVE: To validate a protocol assessing upper limb kinematics using a planar robot among stroke patients. DESIGN: Prospective cohort study. SUBJECTS: Age-matched healthy subjects (n = 25) and stroke patients (n = 25). METHODS: Various kinematic indices (n = 44) were obtained from 4 tasks performed by subjects with REAplan, a planar end-effector robotic device. The metrological properties of this protocol were studied. RESULTS: In stroke patients, 43 kinematic indices showed moderate to excellent reliability (intraclass correlation coefficients (ICC) range 0.40-0.95; and minimal detectable changes range 9.9-121.1%). In healthy subjects, 25 kinematic indices showed moderate to excellent reliability (ICC range 0.40-0.91) and 3 indices showed a laterality effect (p < 0.05). Many of these indices (27 of 44) were altered in stroke patients in comparison with healthy subjects (p < 0.05). The Box and Block test (manual dexterity) and Upper Limb Sub-score of the Fugl-Meyer Assessment (motor control) showed moderate to good correlations with, respectively, 13 and 4 indices (r > 0.40). Finally, a principal component analysis allowed the elaboration of a short version of the protocol, reducing the number of indices to 5 (i.e. Amplitude, CVstraightness, Speed Metric, CVjerk metric and CVspeed metric). CONCLUSION: This study provides a standardized, valid, reliable and sensitive protocol to quantify upper limb impairments in stroke patients, using a planar robot.

Dynamics of revolution time variability in cycling pattern: voluntary intent can alter the long-range autocorrelations.

Long-range dependency has been found in most rhythmic motor signals. The origin of this property is unknown and largely debated. There is a controversy on the influence of voluntary control induced by requiring a pre-determined pace such as asking subjects to step to a metronome. We studied the cycle duration variability of 15 men pedaling on an ergometer at free pace and at an imposed pace (60 rpm). Revolution time was determined based on accelerometer signals (sample frequency 512 Hz). Revolution time variability was assessed by coefficient of variation (CV). The presence of long-range autocorrelations was based on scaling properties of the series variability (Hurst exponent) and the shape of the power spectral density (α exponent). Mean revolution time was significantly lower at freely chosen cadence, while values of CV were similar between both sessions. Long-range autocorrelations were highlighted in all series of cycling patterns. However, Hurst and α exponents were significantly lower at imposed cadence. This study demonstrates the presence of long-range autocorrelations during cycling and that voluntary intent can modulate the interdependency between consecutive cycles. Therefore, cycling may constitute a powerful paradigm to investigate the influence of central control mechanisms on the long-range interdependency characterizing rhythmic motor tasks.